Some vehicle engine systems utilizing direct in-cylinder injection of fuel include a fuel delivery system that has multiple fuel pumps for providing suitable fuel pressure to fuel injectors. This type of fuel system, Gasoline Direct Injection (GDI), is used to increase the power efficiency and range over which the fuel can be delivered to the cylinder. GDI fuel injectors may require high pressure fuel for injection to create enhanced atomization for more efficient combustion. As one example, a GDI system can utilize an electrically driven lower pressure pump (e.g., a fuel lift pump) and a mechanically driven higher pressure pump (e.g., a direct injection pump) arranged respectively in series between the fuel tank and the fuel injectors along a fuel passage. In many GDI applications the lift fuel pump initially pressurizes fuel from the fuel tank to a fuel passage coupling the lift fuel pump and direct injection fuel pump, and the high-pressure or direct injection fuel pump may be used to further increase the pressure of fuel delivered to the fuel injectors. GDI fuel systems typically rely on an estimate of the inlet fuel temperature in order to set a GDI pump inlet pressure. If the estimated fuel temperature is inaccurate, the GDI pump inlet pressure can fall below a fuel vapor pressure, reducing engine performance and efficiency and potentially degrading DI pump durability. On the other hand, compensating for an unreliable fuel temperature by operating the GDI pump at excessively high pressures can increase power consumption and decrease fuel economy.
In one example, shown by Barra et al. in U.S. Pat. No. 8,365,585, a fuel temperature in a common rail injection system is estimated based on a fuel temperature measurement with a temperature sensor positioned in a first fuel line. The common rail injection system temperature is estimated utilizing a complex multi-functional model requiring measurements of engine cooling water temperature, inlet air temperature, vehicle driving velocity, fuel flow speed in the common rail, and fuel pressure in the common rail.
However, the inventors herein have identified potential issues with the approach of Barra et al. First, Barra's model introduces many sources of measurement error because it relies on measurement of several parameters. Furthermore, the model is constructed from at least eight empirical functions, requiring estimation of a multitude of experimental parameters, each of which introduces its own inherent uncertainty into the model. Accordingly, Barra's model may be unreliable and inaccurate because of the cumulative measurement error and inherent uncertainties in the empirical parameters, in particular, when the engine operation spans a wide range of operating conditions and empirical models tend to break down. Further still, in response to these types of conventional fuel temperature estimation models, which exhibit substantial inaccuracies, estimates of fuel temperatures are conservatively higher than actual fuel temperatures. Higher fuel temperature estimates result in higher fuel injection pressures so as to maintain engine performance, albeit sacrificing fuel economy.
In one example, the above issues may be at least partially addressed by a method, comprising, adjusting operation of a low-pressure fuel pump based on a fuel temperature indicated from a rate of change in a pressure of a fuel passage between the low-pressure fuel pump and a high-pressure fuel pump during a first condition, including when the low pressure fuel pump is switched off. In this way, a change in temperature of a volume of fuel may be computed from a measured pressure change in the volume of fuel that is directly related to the volume of fuel and any fuel volume gain or loss.
In this way, the technical effect of determining a fuel temperature accurately and reliably from a rate of change in the fuel pressure can be achieved. Furthermore, a fuel temperature model based on a measured fuel pressure and fuel volume may be constructed with greater accuracy relative to conventional models. Furthermore, the methods and systems described herein can determine the fuel temperature while reducing a reliance on other measured parameters. Further still, more accurately and reliably determining the fuel temperature can enable operation of the fuel system at lower fuel injection pressures, thereby reducing engine fuel consumption.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.